This invention relates to a device for plotting points having a given angular and distance relationship with a reference point.
Tachymetry is a technique used in surveying whereby measurements of the bearing and distance of a remote point relative to a survey station are carried out optically by a single instrument. This technique is becoming increasingly common and more accurate due to the availability of electronic distance measuring instruments capable of measuring distances to a hitherto unobtainable accuracy. Thus there is a requirement for an inexpensive plotting device for use on the drawing board which is capable of plotting simultaneously distances and angles obtained from tachymetric measurements, the angular accuracy being better than the normal half or quarter of a degree obtainable from a simple circular protractor.
There are some known plotters available, covering a full 360 degree range, but these are relatively expensive and generally used in conjunction with telemetering instuments. They are therefore only used by organisations in which tachymetric methods of surveying are in constant use.
Another known device is a simple plotting protractor in the form of a printed card with a circular opening of about 500 mm diameter and angular graduations around the circumference of the opening. The protractor is placed on the drawing surface and points plotted within the circular opening. Some care is needed in positioning the opening centrally with respect to the reference point since the protractor itself has no physical central mark. No radial distance scale is provided and accuracy generally does not exceed 1/4 degree of arc.